The proposed project involves: the synthesis of certain key analogs as a test of a new structure-function model we recently proposed (Proc. Nat. Acad. Sciences USA, 71, 4194 (1974)); the refinement of this model through further structural and biological studies; the continuation and development of proton and carbon-13 magnetic resonance studies of vitamin D-like substances (Science, 186, 939 (1974) and J. American Chem. Soc., 97, 4980 (1975)); and the development of new synthetic routes to vitamin D analogs not involving photochemical steps. The general goals of the project include the development of an understanding of the mechanism of action of vitamin D and the synthesis of potentially useful analogs with high vitamin D or anti-vitamin D activity. BIBLIOGRAPHIC REFERENCES: Anthony W. Norman, Manindra N. Mitra, William H. Okamura and Richard M. Wing, Vitamin D: 3-Deoxy-1alpha-hydroxyvitamin D3, A Biologically Active Analog of 1alpha, 25-Dihydroxyvitamin D3. Science, approximately 188, 1013-1015 (1975). Richard M. Wing, William H. Okamura, Albert Rego, Marcel R. Pirio and Anthony W. Norman, Studies on Vitamin D and its Analogs. VII. Solution Conformations of Vitamin D3 and 1alpha, 25-Dihydroxyvitamin D3 by High Resolution Proton Magnetic Resonance Spectroscopy, J. Amer, Chem. Soc., 97, 4980-4985 (1975).